Dissolution kinetics of ulexite in acetic acid solutions

Ulexite is an important boron mineral used for the production of boron compounds. The aims of this study are to examine the dissolution kinetics of ulexite in acetic acid solutions, and to present an alternative process to produce boric acid. In order to investigate the dissolution kinetics of ulexite in acetic acid solutions, the concentration of solution, reaction temperature, solid-to-liquid ratio, and particle size were selected as experimental parameters. It was determined that the dissolution rate of ulexite increased with increasing solution concentration and temperature and decreasing particle size and solid-to-liquid ratio. The activation energy of the process was found to be 55.8 kJ/mol.     

The mechanical properties of directionally solidified aluminum-based eutectic castings

Abstract

The mechanical properties for directionally solidified Al-Al₃Ni, Al-Si, and Al-Al₂Cu eutectic castings have been determined and it is shown that the properties of castings (solidified at approximately 80 cm/hour) compare favourably to those obtained for slowly solidified eutectics (solidified at approximately 2 cm/hour). The strengths of Al-Al₂Cu and Al-Si eutectic castings are higher than those obtained for slowly solidified alloys while the strengths for the Al-Al ₃Ni eutectic castings are somewhat lower than for the slowly solidified alloys. The Al-Al₃Ni and Al-Al₂Cu cast eutectics essentially maintain their yield strength up to 300°C whereas the yield strength of the Al-Si eutectic decreases continuously with increasing temperature. It is concluded that the high strengths reported result from a combination of the fine micro-structure obtained from the relatively rapid solidification rate and by strengthening of the intermetallic phase.

Réesumé

Les auteurs ont déterminé les propriétés mécaniques d'alliages eutectiques Al-Al₃Ni, Al-Si et Al-Al₂;Cu solidifiésdirec-tionnellement. Ils montrent que les propriétés des coulées (solidi-fiées à environ 80 cm/h) se comparent favorablement à celles d'eutectiques solidifiés lentement (à environ 2 cm/h). Les résistances mécaniques des coulées eutectiques de Al-Al ₂Cu et Al-Si sont plus élevées que celles obtenues pour des alliages solidifiés lentement tandis que les résistances mécaniques des coulées eutectiques Al-Al₃Ni sont légèrement plus basses que celles des alliages solidifiés lentement. Les limites d'élasticité des alliages eutectiques coulés d'Al-Al₃Ni et Al-Al₂;Cu demeurent élevées jusqu 'à des tempéraptures de 300°C, tandis que lalimite d'élasticité de l'alliage eutec tique Al-Si diminue continuellement quand la température croft. Les auteurs conc1uent que les bonnes propriété s mécaniques obtenues ré sultent de la combinaison de l'effet de la microstructure fine produite par le taux de solidification relativement élevéet de l'effet de fibres produit par la phase intermétallique.     

西藏某地钠硼解石制取硼酸的研究

本文以西藏某地钠用解石矿为原料，利用酸法一步直接制取硼酸产品，硼酸单程收率达81．09％、产品纯度达GB538－82指标。     

多参数跟踪装置研究盐和复盐溶解动力学

采用微机与多台分析仪联机装置，测定了钠硼解石溶解过程中Ｎａ＾＋，Ｃａ＾２＋电位及ｐＨ值、电导率值的变化，改进联机装置为一机多用的采集系统，并对氯柱硼镁石在水中溶解的Ｍｇ＾２＋，Ｃｌ＾－，Ｈ＾＋电位等进行自动采样、储存、打印，编制了动力学所需数据处理程序，可进行电极校正，将测定值直接校为浓度，作出Ｃ－Ｔ的动力学曲线及计算动力学方程等，所得结果表明该装置对反庆快或体系均能同步而且准确地得出多种参数的实     

Mechanism of Selective Flotation of Sodium-Calcium Borates with Anionic and Cationic Collectors

Abstract

The major boron minerals, colemanite and ulexite, are frequently found together in boron deposits. Similarities in their chemical compositions create problems in the selective flotation of these minerals. The surface properties of the above boron minerals have been determined by solubility, microflotation, and zeta potential measurements using typical anionic and cationic surfactants. The isoelectric point (iep) of colemanite is 10.5, while ulexite exhibits no iep in a practical pH. Anionic surfactants thus easily float colemanite but fail to float ulexite at a natural pH. This knowledge is used to find the optimum conditions for the selective separation of colemanite from ulexite at a natural pH of 9.3. Cationic surfactants work well but are adversely affected by the presence of clay-type minerals in the boron ore which hinder the floatability of borates by the formation of a slime coating. The mechanism of slime coating onto boron minerals is also elucidated.     

An investigation on the production of sodium metaborate dihydrate from ulexite by using trona and lime

In this study, it was investigated the optimum conditions (extraction temperature and extraction period) for the production of sodium metaborate dihydrate (NaBO₂.2H₂O) by the reaction of ulexite (NaCaB₅O₉·8H₂O) with trona (NaHCO₃-Na₂CO₃·2H₂O) and lime (CaO). The optimum extraction conditions were determined as 50 °C and higher temperature; 6 h and longer extraction time. The characterizations of the product (sodium metaborate dihydrate crystals) were performed by thermogravimetric (TG-DTG) and X-ray diffraction (XRD) analyses. In addition, the percent purity of the product was found to be 96% by using a conductometric method.     

Leaching kinetics of ulexite in sodium hydrogen sulphate solutions

The aim of this study was to investigate the dissolution kinetics of ulexite in sodium hydrogen sulphate solutions in a mechanical agitation system and to declare an alternative reactant to produce boric acid. Reaction temperature, concentration of sodium hydrogen sulphate solutions, stirring speed, solid/liquid ratio and ulexite particle size were selected as parameters of the dissolution rate of ulexite. The experimental results were successfully correlated by linear regression using Statistica program. Dissolution curves were evaluated in order to test shrinking core models for solid-fluid systems. It was observed that increase in the reaction temperature and decrease in the solid/liquid ratio cause an increase in the dissolution rate of ulexite. The dissolution extent is highly increased with increase in the stirring speed rate between 100 and 700 rpm experimental conditions. The activation energy was found to be 36.4 kJ/mol. The leaching of ulexite was controlled by diffusion through the ash or product layer. The rate expression associated with the dissolution rate of ulexite depending on the parameters chosen may be summarized as: 1–3(1 − X)^2/3 + 2(1 − X) = 6.17 × C^0.97 × W^1.17 × D^−1.72 × (S/L)^−0.66 × e^(−36.4/RT)·t.     

Dissolution kinetics of calcined ulexite in ammonium carbonate solutions

The leaching kinetics of calcined ulexite in ammonium carbonate was studied in this work. The effect of parameters of ammonium carbonate concentration, solid/liquid ratio, stirring speed, calcination temperature and reaction temperature was determined in the experiments. It was found that the conversion rate increased with increasing ammonium carbonate concentration, reaction temperature and decreasing solid/liquid ratio. However, the effect of stirring speed on the conversion rate was insignificant. The experimental data practised the heterogeneous and homogeneous models, and an acceptable model for the conversion rates of ulexite was determined to be a first-order pseudohomogeneous reaction model. The activation energy of dissolution process was determined to be 35.3 kJ/mol.     

Determination of Optimal Conditions for Retention of Sulfur Dioxide by Waste Ulexite Ore in an Aqueous Medium

The main aim of this study was to remove sulfur dioxide (SO₂), which is one of the most significant air pollutants emitted from thermal power stations, using waste ulexite ore, which cannot be recycled industrially and poses a risk for the environment. In experiments conducted at atmospheric pressure in an aqueous environment, the optimization of holding SO₂ with waste ulexite ore has been investigated comprehensively and determined how much SO₂ could be retained in solid waste. The Taguchi method was used to determine the optimal conditions, and the effectiveness of the parameters was identified by variance analysis. The selected parameters and their ranges were defined as temperature (293–333?K), solid to liquid ratio (0.4–0.6?g?mL^?1), particle size (150–600?µm), time (10–30?min), pH (5.5–7.5), and stirring speed (350–800?rpm). The optimal conditions for these parameters were determined to be 333?K, 0.45?g?mL^?1, ?250?µm, 15?min, pH 6, and 350?rpm, respectively. Among all the parameters, temperature and pH were found to be the most effective. The results of the study revealed that SO₂ can be retained in solid waste with calcium content of the boron minerals as CaSO₃?·?0.5H₂O and nearly whole B₂O₃ in the waste ulexite passes into solution. Under the optimum conditions, 86% of B₂O₃ passed into the solution and 75.2?L SO₂ was retained by 1?kg waste ulexite ore. Thus, both B₂O₃ recovery and SO₂ removal were materialized, while waste ulexite ore was evaluated and removed, simultaneously.